On demand machine rimpull adjustment to prevent tire slip

ABSTRACT

A system for proactively controlling rimpull limit of a machine includes a hydraulic system having a lift cylinder to move an implement; a lift cylinder pressure sensor that senses a hydraulic pressure of the lift cylinder and responsively produces a lift cylinder pressure signal; and a controller in operable communication with the power train and the lift cylinder pressure sensor. The controller is configured to receive the lift cylinder pressure signal; determine the rimpull limit based at least in part upon the lift cylinder pressure signal; and adjust the torque of the power train to the rimpull limit.

TECHNICAL FIELD

The present disclosure generally relates to machine systems for use on amachine to limit the rimpull of the machine on demand.

BACKGROUND

Generally in a machine, such as a wheel loader and the like, utilizingan implement based hydraulic system, it is desired to have the engineoperating at a high engine speed to ensure proper operation of thehydraulic implement. Often this high engine speed, while desirable foroperation of the hydraulic implement, provides too much torque to thedrive train of the machine, wherein this torque can cause wheel slippageand increased tire wear.

When using the machine to push or move a pile of material with animplement, to prevent tire slip, the machine operator must lift or pushinto the pile to generate downforce on the tires. An inexperiencedoperator may lift too early, causing the implement to ride up and overthe material, or lift too late, causing the tires to slip and wearprematurely.

One method to prevent wheel slip and tire wear is by controlling therimpull of the machine though an adjustment of available torque to thedrive train. Rimpull is generally defined as the force available at thewheels to move a wheeled machine forward. Traditional methods ofcontrolling the rimpull are generally selected by or utilized by anoperator of the machine prior to using the implement for lifting andmoving. This type of system based upon operator selection prior to doingwork has inherent drawbacks. A machine system is desired for adjustingmachine rimpull proactively and on demand based upon machine operatingparameters.

SUMMARY OF THE INVENTION

In accordance with one aspect of the disclosure, a machine system forproactively controlling and limiting rimpull on a machine is disclosed.The machine includes an implement and a power train with an engineproducing torque. The implement is in operable communication with ahydraulic system including a lift cylinder to move the implement. Thelift cylinder having a pressure with a sensor adapted to sense thepressure of the lift cylinder and responsively produce a lift cylinderpressure signal. A controller is in operable communication with thepower train and lift cylinder pressure signal and configured todetermine a rimpull limit based upon the pressure within the liftcylinder and correspondingly and proactively modify the torque to thisrimpull limit. Accordingly, the rimpull limit will be varied accordingto the pressure placed on the lift cylinder by the implement.

In another embodiment of the first aspect of the disclosure, the machinesystem includes a lift position sensor and tilt position sensorproducing a lift position signal and a tilt position signalcommunicating the lift position and the tilt position of the implement,wherein these positions are used by the controller to further limit therimpull.

In another embodiment of the first aspect of the disclosure, thecontroller receives an input from a user or supervisory controllerrelated to a coefficient of friction for a given surface the machine isoperated upon. Accordingly, a user or supervisory controller can utilizethe input to further refine the rimpull limit for a given surface.

In another embodiment of the disclosure for a machine system that isadapted to control tire slip in a machine. The machine includes animplement, a power train including an engine, a wheel having a tire inoperable communication with the power train, and a rimpull. Theimplement is in communication with a hydraulic system including a liftcylinder having a pressure and operably connected to the implement togenerally move the implement. A lift cylinder pressure sensor sensingthe pressure of the lift cylinder and responsively producing a liftcylinder pressure signal. A controller is in operable communication withthe lift cylinder pressure signal and configured to determine adownforce on the wheel based upon the lift cylinder pressure signal andproactively modify the rimpull in proportion to the pressure.

In another embodiment of the present disclosure, the machine systemincludes a lift position sensor and a tilt position sensor. The liftposition sensor and the tilt position sensor responsively producing alift position signal and a tilt position signal related to the positionof the implement. The control in operable communication with the liftposition signal and the tilt position signal and configured to determinethe downforce on the wheel based upon the lift cylinder pressure signal,lift position signal, and tilt position signal and proactively modifythe rimpull in proportion to the signals.

In another embodiment of the present disclosure, a method fordetermining an on demand rimpull limit for a machine is disclosed. Themethod discloses the steps of sensing the hydraulic pressure of a liftcylinder in operable communication with an implement and determining therimpull limit based upon the pressure signal. The rimpull limit is thenused to reduce a torque transmitted through the power train accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general schematic view of an exemplary embodiment of asystem constructed in accordance with the teachings of this disclosure;

FIG. 2 is a perspective view of an embodiment of an exemplary vehicle inwhich a system in which the teachings of the disclosure may be used; and

FIG. 3 is a flowchart illustrating exemplary blocks of an exemplarymethod for preventing tire slip in a machine, in accordance with theteachings of this disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, and with reference to FIG. 1 and FIG. 2,there is shown a machine system of the present disclosure and generallyreferred to by reference numeral 100. The machine system 100 maycomprise one or more wheels 210, a power train 102, a hydraulic system103, an engine, 104, an implement 211, and a controller 106.

In FIG. 2, an exemplary machine 200, a wheel loader, which incorporatesthe features of the present invention is shown. The machine 200 includesa frame 201 generally supporting the various assemblies and mechanicalsystems of the machine 200. The frame 201 supporting a cab assembly 202,axel assemblies 203, a lift assembly 204, and a tilt assembly 205.

The lift assembly 204 and tilt assembly 205 are pivotally mounted on themachine 200 and in operable communication with the implement 211,wherein the movement of the lift assembly 204 and tilt assembly 205 istranslated to the implement 211 in the form a change in a height or anangular tilt of the implement 211. Within this exemplary machine 200,the implement 211 is depicted as a bucket, although other implement 211types may be utilized.

The axel assemblies 203 are in operable communication with the wheels210 and in operable communication with the engine 104, wherein rotationof the axel assemblies 203 and wheels 210 is generally powered by theengine 104 through engagement with the power train 102.

The cab assembly 202 may include a plurality of control devices in theform of joysticks, pedals user interfaces, controls and other types ofdisplay and input devices to provide input to the controller 106.

While the description and drawings are made with reference to themachine system 100 positioned on a wheel loader, the teachings of thedisclosure may be implemented on other machines utilized in earthmoving, mining, construction, farming, material handling,transportation, and other similar machines. Accordingly, as a wheelloader is shown, the machine may be a bulldozer or other type ofmachine.

Referring now back to FIG. 1, the machine system 100 of the presentdisclosure, the hydraulic system 103 includes a lift cylinder 130 inoperable communication with the lift assembly 204 (FIG. 2), wherein thelift cylinder 130 is generally adapted to actuate the lift assembly 204to change a height of the implement 211 and in the form of a linkage.The lift cylinder 130 may be a rod and cylinder assembly as is known inthe art, wherein the lift cylinder 130 generally receives a pressurizedfluid from the hydraulic system 103 to actuate the lift assembly 204.

A lift cylinder pressure sensor 131 is deposed on the machine 200 tosense the pressure within the lift cylinder 130 and generate aresponsive signal for input into the controller 106. The signal from thelift cylinder 130 generally utilized to calculate a downforce on thewheels 210, wherein the lift cylinder 130 sensed pressure is one of theprimary variables used within this calculation. The lift cylinderpressure sensor 131 may be comprised of one or more sensors and beprovided from any sensor type known with the art and suitable for thepurpose of sensing a pressure.

Accordingly, the lift cylinder 130 pressure is used to determine theforce on the wheel 210 during machine 200 work and wherein the machinesystem 100 controller 106 generally adjusts the machine 200 rimpull bydetermining a rimpull limit and and proactively controllingcorresponding power train 102 and engine 104 systems proportionately tothe rimpull limit.

Further, one or more sensors may be disposed on the machine 200 andconfigured as a lift position sensor 240 in operable communication withthe controller 106 to send a responsive signal representative of theposition of the lift assembly 204. Similarly, one or more sensors may bedisposed on the machine 200 and configured as a tilt position sensor 250in operable communication with the controller 106 to send a responsivesignal responsive to the position of the tilt assembly 205.

The controller 106 generally adapted in a most basic form to utilize thelift sensor pressure 130 to determine a limit on the rimpull inproportion to the lift cylinder 130 pressure. Accordingly, this rimpulllimit is controlled by adjusting a torque from the engine 104 throughthe power train 102 and to the wheels 210.

In an advanced implementation, the system 100 of the present disclosureis generally adapted to utilize multiple sensor signals 131, 240, 250 todetermine the downforce on the wheels 210 and limit the rimpullaccordingly.

The following variables are generally utilized in the system 100 withthe below calculations to determine the downforce:

-   -   F_(x): horizontal component of force applied to the implement        tip    -   F_(y): vertical component of force applied to the implement tip    -   F_(cyl): lift cylinder force    -   F₀: lift cylinder force induced by an empty implement lift        assembly and tilt assembly linkage weight    -   ΔF_(cyl): lift cylinder force induced by external force    -   k_(x): lift cylinder force increase due to unit F_(x) horizontal        force    -   k_(y): lift cylinder force increase due to unit F_(y) vertical        force    -   W: machine weight    -   μ: coefficient of friction

The force in the lift cylinder is a composite of force induced by anempty linkage weight and external forces.

F _(cyl) =F ₀ +ΔF _(cyl)

Assuming a fixed point of application (implement tip) the cylinder forceis the sum of the external force vector components and their respectivekinematic gain factors.

Δ F_(cy) = F_(x)k_(x) + F_(y)k_(y)$F_{y} = \frac{{\Delta \; F_{cyl}} - {F_{x}k_{x}}}{k_{y}}$

The gain factors and empty bucket cylinder force are each a function oflift and tilt position which can be expressed as lookup maps.

k _(x) =f ₁(lift,tilt)

k _(y) =f ₂(lift,tilt)

F ₀ =f ₃(lift,tilt)

To avoid slipping the horizontal force must be less than the product ofthe coefficient of friction and the total vertical load on the tires.

F _(x)<μ(W+F _(y))

Substituting for F_(y) and solving for F_(x)

$F_{x} < {\mu ( {W + \frac{\Delta \; F_{cyl}F_{x}k_{x}}{k_{y}}} )}$$F_{x} < {\mu \; \frac{{Wk}_{y} + {\Delta \; F_{cyl}}}{k_{y} + {k_{x}\mu}}}$

Finally substituting for ΔF_(cyl) we have the horizontal force limitexpressed in terms of current cylinder force, linkage position, andassumed coefficient of friction

$F_{xlimit} = {\mu \; \frac{{Wk}_{y} + F_{cyl} - F_{0}}{k_{y} + {\mu \; k_{x}}}}$

Based upon this above calculation, F_(xlimit) is the rimpull limit for agiven machine 200 based upon the system 100. Accordingly, the machine200 can approach a pile with the implement 211 and wherein thecontroller 106 will adjust the rimpull based upon the lift cylinder 130pressure and adjust the rimpull limit as the pressure increases.Accordingly, the rimpull limit is generally adjusted between a range of60% and 100% of the total available rimpull based upon the pressure ofthe lift cylinder 130, although the limit can be reduced below 50%. Asthe pressure sensed 131 on the lift cylinder 130 increases, the rimpulllimit is proportionately increased towards 100% of the total availablerimpull to ensure efficient usage of the machine 200 hydraulic system103.

The controller 106 may receive an input 161 for the coefficient of thefriction (“μ”) within the above calculation. Accordingly, the machine200 operator may make an adjustment to the rimpull limit based upon agiven ground surface, wherein the input 161 is adjusted to the actualfriction of a given surface the machine 200 is operated upon.

Depending on the power train 102 system of a given machine 200 therimpull limit will be adjusted utilizing a different mechanism. For amachine 200 having a power train 102 type with an impeller clutch torqueconverter 120 the controller 106 will control the rimpull limit througha clutch pressure of the impeller clutch 121. For a machine 200 having apower train 102 type with an electric motor with a continuously variabletransmission (“CVT”) 122 the controller 106 will control the rimpulllimit through electric motor current 123. For a machine 200 having apower train 102 powered through hydraulics and having a hydrostatic CVT124 the controller 106 will control the rimpull limit through variatordisplacement 125. For a machine 200 having a power train 102 type with atorque converter 126 the controller 106 will control the rimpull limitthough engine 104 speed.

In use, a user of the machine system 100 on the machine will generallyimplement the system 100 to prevent tire wear where the controller 106will set the rimpull limit on demand based upon the lift cylinderpressure 130 sensed pressure 131. As the user approaches a pile ofmaterial to be moved the rimpull limit is reduced in proportion to thelift cylinder 130 pressure. As there is no material in the implement211, the pressure within the lift cylinder 130 is relatively low and thetorque provided to the wheels 210 is limited. As the user pushes intothe pile with the machine 200 implement 211, the lift cylinder 130pressure increases and the controller 106 correspondingly andproportionately increases the rimpull limit. As material is added to theimplement 211 downforce increases on the wheels 210 and the rimpull nolonger needs to be limited.

INDUSTRIAL APPLICABILITY

Referring now to FIG. 3, an exemplary flowchart is illustrated showingsample method steps that may be followed in setting an on demand rimpulllimit for a machine 200 to prevent tire slip during machine 200 use. Themethod 300 may be practiced with more or less method steps and is notlimited to the order shown. While in the flowchart, the controller 106processes operational parameters to determine if the machine 200 andimplement 211 are doing work, wherein the rimpull of the wheels 210 islimited to prevent tire slip.

The initial method step 301 includes, receiving by a controller 106,operational parameters. The operational parameters may include senseddata related to weight and positioning of the implement 211 and input161 related to the friction of the surface the machine 200 is operatedupon.

In one embodiment of the present disclosure, the controller 106 receivesa pressure signal 131 from the lift cylinder 130. In an alternateembodiment, the controller 106 receives a pressure signal 131 from thelift cylinder 130 and a signal from the position sensor 240 of the liftassembly 204. In an alternate embodiment, the controller 106 receives apressure signal 131 from the lift cylinder 130, a signal from theposition sensor 240 of the lift assembly 204, and a signal from theposition sensor 250 of the tilt assembly.

After the controller 106 receives the given operational parameters atstep 301, the controller 106 identifies, through a calculation, thedownforce needed at at the wheels 210 of the machine 200 to preventwheel 101 slip at step 302.

Based upon this downforce, the controller 10 then limits the rimpull ofthe machine 200 at step 303. Throughout the use of the machine 200, step302 is repeated and wherein step 303 is continually processed on demandto prevent wheel 101 slip during machine 200 use.

1-20. (canceled)
 21. A method for controlling a wheel loader machine,the machine having a hydraulically-driven bucket control systemincluding a lift cylinder and a bucket; and a power train including anengine and producing a torque for moving wheels of the machine, themethod comprising: automatically increasing a force available at thewheels of the wheel loader machine in response to an increase inpressure in the hydraulically-driven bucket control system.
 22. Themethod of claim 21, wherein the increase in pressure results frominteraction of the bucket with a pile of material.
 23. The method ofclaim 21, further including limiting the force available at the wheelswhen the machine is doing work, prior to automatically increasing theforce available at the wheels.
 24. The method of claim 21, wherein theincreasing of the force available at the wheels is proportional to theincrease in pressure in the hydraulically-driven bucket control system.25. The method of claim 21, wherein the increase in pressure in thehydraulically-driven bucket control system corresponds to an increase inpressure in the lift cylinder.
 26. The method of claim 21, wherein theincreasing of the force available at the wheels corresponds to anincreasing of a rimpull limit, and the increasing of the rimpull limitis within a range of 60% and 100% of a total available rimpull.
 27. Themethod of claim 21, wherein the increasing of the force available at thewheels corresponds to an increasing of a rimpull limit, and theincreasing of the rimpull limit includes no longer applying a rimpulllimit.
 28. The method of claim 21, wherein the automatically increasingof a force available at the wheels is based on an input from an operatoror controller regarding the ground surface that the wheel loader isoperated upon.
 29. The method of claim 28, wherein the input regardingthe ground surface is related to a coefficient of friction of the groundsurface.
 30. A method for controlling a machine, the machine having ahydraulically-driven implement control system including a lift cylinderand an implement; and a power train including an engine and producing atorque for moving wheels of the machine, the method comprising:automatically increasing a force available at the wheels in response toat least one of: an increase in pressure in the hydraulically-drivenimplement control system, or movement of the implement by thehydraulically-driven implement control system.
 31. The method of claim30, wherein the automatically increasing of the force available at thewheels is in response to at least: the increase in pressure in thehydraulically-driven implement control system, and the movement of theimplement by the hydraulically-driven implement control system.
 32. Themethod of claim 31, wherein the increase in pressure results frominteraction of the implement with a pile of material.
 33. The method ofclaim 31, wherein the increase in pressure in the hydraulically-drivenimplement control system corresponds to an increase in pressure in thelift cylinder.
 34. The method of claim 31, wherein the movement of theimplement by the hydraulically-driven implement control systemcorresponds to a movement of the lift cylinder.
 35. The method of claim31, wherein the increasing of the force available at the wheelscorresponds to an increasing of a rimpull limit.
 36. The method of claim31, wherein the automatically increasing of the force available at thewheels is based on an input from an operator or controller regarding theground surface that the machine is operated upon.
 37. The system ofclaim 36, wherein the input regarding the ground surface is related to acoefficient of friction of the ground surface.
 38. A system forcontrolling a machine, the system comprising: a hydraulically-drivenimplement control system including a lift cylinder and an implement; apower train including an engine and producing a torque for moving wheelsof the machine; and a controller in operable communication with thehydraulically-driven implement control system, the engine, and the powertrain, the controller being configured to: automatically increase aforce available at the wheels in response to an increase in pressure inthe hydraulically-driven implement control system.
 39. The system ofclaim 38, wherein the increase in pressure results from interaction ofthe implement with a pile of material.
 40. The system of claim 39,wherein the increase in pressure in the hydraulically-driven implementcontrol system corresponds to a sensed increase in pressure in the liftcylinder.